The migration of fines involves the movement of fine clay and/or non-clay particles (e.g. quartz, amorphous silica, feldspars, zeolites, carbonates, salts and micas) or similar materials within a subterranean reservoir formation due to drag and other forces during production of hydrocarbons or water. Fines migration may result from an unconsolidated or inherently unstable formation, or from the use of an incompatible treatment fluid that liberates fine particles. Fines migration may cause the very small particles suspended in the produced fluid to bridge the pore throats near the wellbore, thereby reducing well productivity. Damage created by fines is typically located within a radius of about 3 to 5 feet (about 1 to 2 meters) of the wellbore, and may occur in gravel-pack completions and other operations.
Fines migration is a complex phenomenon governed largely by mineralogy, permeability, salinity and pH changes, as well as drag forces created by flow velocity, turbulence and fluid viscosity, as described in detail in J. Hibbeler, et al., “An Integrated Long-Term Solution for Migratory Fines Damage,” SPE 81017, SPE Latin American and Caribbean Petroleum Engineering Conference, Port-of-Spain, Trinidad, West Indies, 27-30 Apr. 2003, incorporated herein by reference in its entirety. The authors note that mobilization of fines can severely damage a well's productivity, and that fines damage is a multi-parameter, complex issue that may be due to one or more of the following downhole phenomena: (1) high flow rates, particularly abrupt changes to flow rates; (2) wettability effects, (3) ion exchange; (4) two-phase flow, particularly due to turbulence that destabilize fines in the near-wellbore region; and (5) acidizing treatments of the wrong type or volume which can cause fines.
J. Hibbeler, et al. note that fines, especially clays, tend to flow depending on their wettability, and since fines are typically water-wet, the introduction of water may trigger fines migration. However, they note that clay particles may become oil-wet or partially oil-wet, due to an outside influence, and thus the fines and clay particles may become attracted to and immersed in the oil phase. The authors also note that all clays have an overall negative charge and that during salinity decrease, pH increases in-situ due to ion exchange. A pH increase may also be induced via an injected fluid. As pH increases, surface potential of fines increases until de-flocculation and detachment occurs, aggravating fines migration.
Fines fixation has become troublesome during oil and gas production and during many oil and gas recovery operations, such as acidizing, fracturing, gravel packing, and secondary and tertiary recovery procedures. Hydraulic fracturing is a method of using pump rate and hydraulic pressure to fracture or crack a subterranean formation. Once the crack or cracks are made, high permeability proppant, relative to the formation permeability, is pumped into the fracture to prop open the crack. When the applied pump rates and pressures are reduced or removed from the formation, the crack or fracture cannot close or heal completely because the high permeability proppant keeps the crack open. The propped crack or fracture provides a high permeability path connecting the producing wellbore to a larger formation area to enhance the production of hydrocarbons.
Gravel packing is a sand-control method employed to prevent the production of formation sand. In gravel pack operations, a steel screen is placed in the wellbore and the surrounding annulus packed with a gravel of a specific size designed to prevent the passage of formation sand. The goal is to stabilize the formation while causing minimal impairment to well productivity. Operations combining fracturing and gravel packing are termed “frac packs”.
It would be desirable if methods and/or compositions would be devised to help fix or stabilize fines within a subterranean formation so that their migration is reduced, inhibited or eliminated.